CA2365256A1

CA2365256A1 - Lubricant composition containing tin disulfide

Info

Publication number: CA2365256A1
Application number: CA002365256A
Authority: CA
Inventors: Volker Von Drach; Karl-Heinz Hensel; Dieter Guhl
Original assignee: Individual
Current assignee: SETRAL CHEMIE GmbH
Priority date: 1999-03-03
Filing date: 2000-03-02
Publication date: 2000-09-08
Also published as: DE19909352A1; EP1159379A1; KR20020009569A; WO2000052116A1; JP2002538265A

Abstract

The invention relates to a lubricant composition which contains a solid lubricant with a layered lattice structure consisting of 70 to 100 percent by weight tin disulfide. The lubricant composition possesses excellent lubricating and wearing properties.

Description

LUBRICANT COMPOSITION
The present invention relates to a lubricant composition, in particular a liquid or semisolid lubricant composition, which contains tin disulfide (berndtite, mosaic gold, hexagonal crystal structure) as the only or predominant solid lubricant having a layer lattice structure.
In lubricants for industrial applications, the solid lubricant components used are in particular molybdenum disulfide (MoSa), graphite and polytetrafluoroethylene (PTFE). They are typically used in greases, pastes, low-friction coatings, suspensions, dispersions, mineral and synthetic oils, solvents and water-based cooling lubricants. The solid lubricant should ensure relatively high protection from wear and improve the coefficients of friction.
Depending on the application, these solid lubricants have disadvantages which limit their field of use.
Thus, for example, PTFE are stable only up to 250°C and molybdenum disulfide up to about 350°C, whereas graphite has no additional separation effect and both graphite and molybdenum disulfide can be used only to a limited extent in the food sector owing to their dark color.
Use of other heavy metal sulfides has also been considered. Thus, GB 956 568 describes a solid lubricant composition which, in addition to a first sulfide component, such as molybdenum disulfide, contains a second sulfide component, such as tin disulfide in an amount of up to 30~ by weight. The tin disulfide improves the wear and lubricating properties of molybdenum disulfide. However, it is emphasized that tin disulfide is not the optimum additive and is a poorer lubricant than molybdenum disulfide.

CH 644 890 describes a lubricant which contains a mixture of from 60 to 90~ by weight of graphite and from 10 to 40~ by weight of a metal sulfide, such as molybdenum disulfide or tin disulfide. It is found that when mixtures of graphite and molybdenum disulfide are used at above 200°C the coefficient of friction increases sharply.
EP 108 892 A describes a solid construction material having good low-friction properties for use in mechanical engineering, which contain from 20 to 80~ by weight of a metal sulfide, such as molybdenum disulfide or tin disulfide, and from 80 to 20~ by weight of graphite. The shaped articles produced from the construction materials have good low-friction and corrosion properties.
EP 654 616 describes a friction lining mixture for brake and clutch linings which contains tin sulfide or tin disulfide as a solid lubricant. The use of tin sulfide leads to an improvement in the wear of the mating pairs and to a decline in the susceptibility to cracking of the counterpart to the friction lining and to an improvement in the lubricating functions at temperatures above 400°C. WO 99/52997 describes a solid lubricant comprising a tin sulfide matrix of a plurality of tin sulfides and carbon embedded therein.
The solid lubricant is used in friction linings.
DE 15 94 367 A describes a process for the preparation of an oleophilic solid lubricant by milling a mixture of graphite, sulfur, mixtures of metal powders and sulfur and covalent or ionic metal sulfides in an organic liquid, for example a hydrocarbon, to a BET
surface area of from 10 to 800 mz/g.
DE 16 67 833 A describes oleophilic tin sulfides which are prepared by milling a tin sulfide in an organic liquid, such as a hydrocarbon, in the absence of air, until the tin sulfide has a BET surface area of from 5 to 400 m2/g. The oleophilic tin sulfide can be used as a solid lubricant and has an improved load-bearing capacity compared with conventional SnSZ.
Lubricant compositions comprising molybdenum disulfide or graphite as a solid lubricant have the disadvantage that their resistance to wear at high temperatures as well as at low temperatures is unsatisfactory.
Moreover, their use leads to very dark compositions, which is frequently undesirable. The use of other metal sulfides in turn results in lubricant compositions whose lubricating properties are frequently unsatisfactory.
It is an object of the present invention to provide a lubricant composition which has both good lubricating properties and high resistance to wear. Moreover, the lubricant composition should not be substantially darker than the lubricant base.
We have found that this object is achieved if from 70 to 100 by weight of tin disulfide are used as a solid lubricant in a solid and in particular in a liquid or semisolid lubricant composition.
The present invention therefore relates to a lubricant composition which contains a solid lubricant having a layer lattice structure and comprising from 70 to 100$
by weight, based on the total weight of the solid lubricant having a layer lattice structure, of nonoleophilic tin disulfide.
The tin disulfide (SnSz) may also be present as a mixture with at least one other tin sulfide, such as SnS, Sn2S3 (tin(II,IV) mixed sulfide) and Sn3S4. Mixtures o f SnS2 and SnS ; o f SnSz and Sn2 S3 ; and o f SnSa , SnS and Sn2Ss are preferred. The amount of SnSa in a mixture with another tin sulfide is in general from 70 to 99.5 by weight, based on the total weight of the mixture.
The lubricant composition is preferably carbon-free.
Preferably, the solid lubricant having a layer lattice structure comprises from 80 to 100, particularly preferably from 90 to 100, ~ by weight of tin disulfide or of said mixture, based in each case on solid lubricant having a layer lattice structure.
The novel lubricant composition may be present in solid form, for example as a powder, in semisolid form, for example as a paste, or in liquid form, for example as a dispersion or suspension. A liquid or semisolid lubricant composition is preferred.
The amount of solid lubricant having a layer lattice structure in the lubricant composition varies depending on the form and use of the composition. In the case of a liquid lubricant composition, this amount is in general from 0.5 to 20, in particular from 1 to 10, $
by weight, based on the total weight of the composition. In the case of a semisolid lubricant composition, this amount is in general from 15 to 80, in particular from 20 to 70, ~ by weight. In the case of a solid lubricant composition, this amount is in general from 10 to 100, preferably from 20 to 100, or from 50 to 100, ~ by weight of the composition.
The novel liquid lubricant compositions contain the tin disulfide suspended or dispersed in a liquid, which is chosen according to the intended use. Such liquids (lubricant bases) are known to a person skilled in the art and are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A 15, 429-443, 1990. Examples of such liquids are Mi4oo3s - mineral oils, - synthetic oils, for example synthetic hydrocarbons, such as polyolefin oils, chlorinated 5 hydrocarbons or hydrocarbon oils obtained by hydrocracking (isoparaffins), polyether oils, ester oils, phosphoric esters, silicone oils, etc.
- vegetable oils, such as rapeseed oil or linseed oil.
Polyolefin oils which may be used are in particular polymers of Ca-Clz-a-olefins .
Polyether oils include aliphatic polyether oils, such as poly(alkylene glycols), e.g. polyethylene glycol, polypropylene glycol and copolymers thereof, and the mono- and diethers, ester-ethers and diethers thereof.
Water-soluble and water-insoluble types are suitable.
Aliphatic polyether oils include perfluoropolyalkyl ethers.
Preferred polyether oils are polyphenyl ethers.
The ester oils are in particular the following ester types:
a) esters of branched primary alcohols with straight-chain dicarboxylic acids;
b) esters of branched monocarboxylic acids with straight-chain diols or poly(alkylene glycols);
c) esters of straight-chain primary alcohols with branched dicarboxylic acids; and d) esters of neopentylpolyols with monocarboxylic acids.
Of particular importance are the above esters a) and the so-called complex esters of dicarboxylic acids and glycols or polyglycols, which have terminal groups of monocarboxylic acids or monoalcohols. Branched primary alcohols are in particular the alcohols obtained by oxo synthesis or aldol condensation, such as 2-ethylhexanol and the C~-, CB- and C9-oxo alcohols. Particularly preferred dicarboxylic acids are sebacic, azeleic and adipic acid. A preferred poly(alkylene glycol) is polyethylene glycol) having a molecular weight of from 100 to 600.
The esters of neopentylpolyols are in particular esters of neopentylglycol, trimethylolethane, trimethylol-propane, pentaerythritol and the ethoxylated and/or propoxylated products thereof.
The ester oils and the polyether oils are preferred according to the invention.
Examples of novel liquid lubricant compositions are motor oils, gear oils, turbine oils, hydraulic fluids, pump oils, heat transfer media, insulating oils, drilling oils, cutting oils, compressor oils, chain oils, glass machine oils, mold oils, armaments or else, cylinder oils, solvent- or water-based low-friction coatings (before evaporation of the carrier liquid), cooling lubricants, etc.
Semisolid novel lubricant compositions are based in general on mineral or synthetic greases and mineral or synthetic oils (as stated above) in combination with suitable thickeners. Examples of semisolid novel lubricant compositions are greases, pastes, carriage greases, roller bearing and sliding bearing greases, etc.
Examples of suitable thickeners are - purely organic thickeners, such as polyureas and polyurethanes, - amorphous or hydrophobic silica, sheet silicates, such as bentonites, which may be rendered hydrophobic, - metal salts, oxides, hydroxides and sulfides and related compounds, in particular metal salts of fatty acids, such as stearic acid or 12-hydroxystearic acid. The metal salts of the fatty acids can be used as a mixture with salts of short-chain carboxylic acids, such as acetic acid or benzoic acid. Cations which may be used are, for example, Li+, Na+, K+, f'az+~ Ba2+~ A13+/
[Al (OH) 2]+, [Al (OH) ] 2+ and Ti02+.
Examples of solid lubricant compositions are low-friction coatings (solvent- or water-based) in the active state, i.e. after evaporation of the carrier liquid, coatings for bearings, plug connections, bulbs, etc. and solid lubricants which serve as additives, for example for friction linings or self-lubricating plastics.
The novel lubricants may contain up to 30~ by weight of other solid lubricants having a layer lattice structure, such as molybdenum disulfide, antimony trisulfide, tungsten disulfide, bismuth trisulfide, lead sulfide, graphite, etc., in addition to tin disulfide. Moreover, they may contain further solid lubricants, such as polytetrafluoroethylene.
The novel lubricant compositions may contain conventional additives, such as antioxidants, viscosity improvers, pour point depressants, detergents, and dispersants (HD additives) and EP (extreme pressure) additives; friction modifiers, antifoams, demulsifiers, corrosion inhibitors, emulsifiers, etc. Useable additives and their use in the respective lubricant compositions are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Volume 15, page 446 et seq.

The tin disulfide used may be any commercially available tin disulfide or tin disulfide prepared by known processes.
According to a preferred embodiment, a tin disulfide which is prepared by precipitation and subsequent heating or by reaction with tin(II) compound or of metallic tin with sulfide, if required under inert gas, without the addition of halogen-containing substances, at from 350 to 750°C, is used. Tin(II) compounds which may be used as starting material are, for example, SnS, SnClz, SnS04 and tin(II) carboxylates, such as tin(II) formate and tin(II) oxalate. The tin disulfide obtained is a homogeneous, golden yellow powder which does not become discolored even at relatively high temperatures.
Mixtures of SnSz, SnS and/or SnzSs can be prepared, for example, by the process described in WO 99/52997.
The preparation of the novel lubricant compositions is effected in a conventional manner by incorporating the tin disulfide into said liquid, semisolid or solid compound with the aid of customary mixing apparatuses.
The novel lubricant compositions have excellent lubricating properties and have resistance to wear which is excellent at both high and low temperatures.
The wear improves substantially compared with analogous lubricant compositions comprising other solid lubricants, especially under load and at relatively high temperatures (for example from 150 to 250°C), while the coefficients of friction are at least comparable. These positive properties are also obtained if, in combinations with other lubricants, tin disulfide constitutes the predominant proportion (from 50 to 100 by weight) of the solid lubricants having a layer lattice structure.

The examples which follow illustrate the invention without restricting it.
Example 1 100 g of tin disulfide were incorporated into 1900 g of mineral oil (mixture of Bright Stock solvent 12~ +
Mouvement 46 88~, sold, for example, by Shell, Esso or Total) with the aid of a mixing apparatus. The resistance to wear of the lubricant composition obtained was then determined at 20°C and 150°C in comparison with a lubricant composition which, instead of tin disulfide, contains the same amount by weight of molybdenum disulfide. The resistance to wear was determined using a frictional wear tester and a rotating ring dipping into the test oil. The ring had a geometry similar to that in the case of the Reichert test, which is described, for example, in the monograph by Molykote (Zechel et al., 1991, 5525). After the lubricant composition had been heated to the desired temperature, the ring was gradually loaded and the wear cap was measured. The results obtained are listed in Table 1 below:

Table 1:
Load Wear ( mm2 (N) ) __ .
A B C D

500 0.79 0.69 0.75 0.63 1000 1.84 1.31 1.87 1.47 1500 2.94 1.37 2.47 1.71 2000 11.44 1.46 13.01 1.84 2500 18.84 1.61 27.67 4.52 3000 20.41 1.71 > 35 30.22 Composition A: mineral oil + 5~ of MoSz at 20°C

Composition B: mineral oil + 5~ of SnSz at 20°C
Composition C: mineral oil + 5~ of MoS2 at 150°C

10 Composition D: mineral oil + 5~ of SnSz at 150°C.
It is clear that the novel compositions surprisingly give significantly better wear values than the composition comprising molybdenum disulfide, both at 20°C and at 150°C. The difference with increase in load is particularly noticeable.
The coefficients of friction were determined using the same compositions and at the same temperatures. The results are contained in Table 2 below:

Table 2:

Load Coefficients (N) of friction A B C D

500 0.100 0.140 0.120 0.098 1000 0.096 0.110 0.089 0.093 1500 0.093 0.110 0.089 0.089 2000 0.089 0.092 0.089 0.071 2500 0.092 0.092 0.091 0.099 3000 0.095 0.095 0.290 0.250 The coefficients of friction for the lubricant composition comprising SnSz at 150°C or at loads from 2000 N are comparable with those for the corresponding composition comprising MoS2. It should be noted that the molar amount of SnSz is lower than that of MoSz owing to the 14~ higher molecular weight.
Example 2 In a comparable test series, a perfluorinated alkyl polyether (viscosity at 40°C: 500 mmz/s) comprising 5~
by weight of SnSz was compared with the same lubricant which, instead of SnSz, contained the same amount by weight of MoSz, PTFE or graphite. The test series was carried out at 250°C.
The results are contained in Table 3 below.

Table 3:

Load Wear (mm2 (N) ) SnSz MoS2 PTFE Graphite 500 1.0 0.9 2.1 1.8 1000 2.8 3.3 3.5 3.3 1500 2.9 4.5 4.5 4.4 2000 3.1 5.8 5.8 6.4 2500 5.0 6.2 26.5 10.2 Compared with all other solid lubricants, SnSa has better wear values, which is very clear in particular at loads from 1000 N.
Example 3 2~ by weight of SnSa were used, in a synthetic oil (ester) employed as chain oil, for lubricating chains in the high temperature range up to more than 250°C.
The power consumption, which increases with increasing coefficient of friction, is still 1.85 kWh/h after lubrication. After 48 hours, the power consumption increases to 1.95 to 2 or more kWh/h if no SnSz is used, owing to the loss of lubrication. After lubrication with the novel combination, the power consumption remained at 1.85 kWh/h even after 48 hours. This illustrates the considerable importance of the novel lubricants in practice.

Claims

claims

1. A carbon-free solid lubricant composition containing a solid lubricant having a layer lattice structure and comprising from 70 to 100%
by weight of nonoleophilic tin disulfide (based on the total weight of the solid lubricant).

2. A lubricant composition in liquid or semisolid form, containing a solid lubricant having a layer lattice structure and comprising from 70 to 100%
by weight of nonoleophilic tin disulfide or a mixture of tin disulfide with at least one other tin sulfide, excluding a composition which contains tin disulfide in paraffin oil or in a mineral oil having a Redwood viscosity of 160 sec.
at 60°C and a viscosity index of 95.

3. A composition as claimed in claim 1 or 2, wherein the solid lubricant comprises from 80 to 100% by weight of tin disulfide.

4. A composition as claimed in any of claims 1 to 3, which comprises, as the solid lubricant, a mixture of SnS2 and Sn2S3 and, if required, SnS and further tin sulfides.

5. A composition as claimed in claim 4, wherein the mixture comprises from 80 to 99% by weight, based on the total weight of the mixture, of SnS2.

6. A composition as claimed in any of claims 2 to 5, wherein the solid lubricant is suspended in a synthetic oil.

7. A composition as claimed in claim 6, wherein the synthetic oil is selected from ester oils, polyether oils, phosphoric esters, silicone oils and synthetic hydrocarbons.